The present invention relates to the field of adsorption filter technology.
The present invention more particularly relates to adsorptive molded parts obtainable particularly from adsorptive structures based on agglomerates of adsorbent particles, and to a process for their production and their use.
The present invention further relates to filters comprising the adsorptive molded parts of the present invention.
To clean or purify fluidic media, more particularly gases, gas streams or gas mixtures, such as air for example, or alternatively liquids, such as water for example, particulate systems based on particles with specific activity (e.g., adsorbents, ion exchangers, catalysts, etc) are often used.
For instance, the use of adsorbent particles to remove toxic or noxiant substances and odors from gas or air streams or else from liquids is known from the prior art.
The use of loose beds of the aforementioned particles, particularly in she form of loose granular-bed filters, is the central form whereby the particles concerned, such as adsorbent particles for example, are brought into contact with the gas or liquid concerned.
Since small particles, such as adsorbent particles for example, provide a larger surface area than larger particles, efficiency is, not unexpectedly, better with the comparatively small particles. However, the small particles in a loose bed lead to a high pressure drop and, what is more, promote the formation of channels, which entails a certain risk of breakthrough. Therefore, the particle size used in loose beds is often but a compromise, meaning that usually the particle sizes optimal for the particular application cannot be used. More particularly, the need to achieve economical operating conditions, more particularly an acceptable pressure drop, often means that larger particles (e.g., adsorbent particles) come to be used than would be desirable for optimal utilization of the adsorption efficiency, so that it is often the case that a considerable portion of the theoretically available capacity cannot be used.
DE 38 13 564 A1 and the same patent family's EP 0 338 551 A2 disclose an activated carbon filter layer for gasmasks which comprises a highly air-pervious, substantially shape-stable three-dimensional supporting scaffold whereto a layer of granular, more particularly spherical activated carbon particles from 0.1 to 1 mm in diameter is fixed, wherein the supporting scaffold can be a braided structure formed of wires, monofilaments or struts, or be a large-pore reticulated polyurethane foam. One disadvantage with the system described therein is the fact that it requires an additional supporting material which has to be endowed with the particles in question in a relatively costly and inconvenient operation. In addition, the particular choice of supporting scaffold then restricts the use in question.
DE 42 39 520 A1 discloses a high-performance filter which consists of a three-dimensional supporting scaffold whereto adsorbent particles are fixed via a bonding material, wherein the supporting scaffold is sheathed with a thermally stable and very hydrolysis-resistant plastic which amounts to about 20 to 500%, based on the scaffold. More particularly, the supporting scaffold comprises a large-pore reticulated polyurethane foam sheathed with a silicone resin, polypropylene, hydrolysis-resistant polyurethane, an acrylate, a synthetic rubber or fluoropolymers. The manufacturing process for these structures is relatively costly and inconvenient. In addition, the technology described therein requires the presence of an additional supporting structure.
DE 43 43 358 A1 discloses porous bodies comprising activated carbon which consist of plates and agglomerates formed from ground activated carbon incorporated in a porous SiO2 matrix. What is more particularly described therein are porous plates or bodies having adsorbing properties, wherein activated carbon granules or activated carbon spherules, and/or granules or spherules comprising activated carbon, are adhered together by means of a silicate solution and subsequently the silicate bridges are converted into silica gel bridges and the bodies are dried. One disadvantage with this is the fixed geometry of these porous bodies and also their lack of flexibility and compressibility, making them unsuitable for filtering conditions under mechanical loading. A further disadvantage is that the particles comprising activated carbon are completely wetted with the silicate solution, so that a large portion of the capacity of these particles is no longer available for adsorptive processes.
DE 43 31 586 02 discloses activated carbon agglomerates wherein activated carbon particles between 0.1 to 5 mm in diameter are disposed and adhered around an approximately equal-sized particle of pitch by slight pressure and heating and thereafter the pitch particle is rendered infusible and converted into activated carbon by oxidation, so that the free interspace between the particles in the agglomerate has a width amounting to at least 10% by volume of the particle size. One disadvantage with the particles described therein is the relatively costly, high-energy production process and also the incompressibility of the agglomerates obtained. Owing to the rigidity of the activated carbon agglomerates, no use is contemplated for filter applications under mechanical loading. The lack of compressibility also means that further processing into molded parts by compression molding is not possible.
The same applies to the porous bodies having adsorbing properties as per DE 42 38 142 A1, which comprise adsorbent particles which are interconnected via bridges of inorganic material, more particularly argillaceous earth, wherein the void spaces between the adsorbent particles comprise from 10 to 100% of the volume of the adsorbent particles. Again, the porous bodies described therein have but little flexibility and compressibility, foreclosing any use under mechanical loading and any further processing into molded parts by compression molding.